Electrodynamic loudspeaker

Abstract

An electrodynamic loudspeaker which comprises a generally rectangular flat vibrating plate, and first and second magnetic drives for driving the vibrating plate to produce vibrations. The first magnetic drive is so positioned as to drive the vibrating plate at a first location corresponding to one of two line nodes m 1 and m 2 of vibration of a first predetermined frequency f 1 which would be produced when the vibrating plate is driven at the center thereof, whereas the second magnetic drive is so positioned as to drive the vibrating plate at a second location corresponding to one of four line nodes n 1 , n 2 , n 3 and n 4 of vibration of a second predetermined frequency f 3 which would be produced when the vibrating plate is driven at the center thereof. Each of all of the line nodes extends in parallel to the shorter sides of the rectangular shape of the vibrating plate.

What is claimed is: 
     
       1. An electrodynamic loudspeaker having: a generally rectangular flat vibrating plate having two pairs of opposite sides, the sides of one of said pairs being longer than the sides of the other said pair; and   magnetic drive means consisting only of first and second magnetic drives for driving the vibrating plate to produce vibrations, said first magnetic drive being so positioned as to drive the vibrating plate at a first location corresponding to one of two line nodes m 1  and m 2  of vibration of a first predetermined frequency f 1  which would be produced when the vibrating plate is driven at the center thereof, said second magnetic drive being so positioned as to drive the vibrating plate at a second location corresponding to one of four line nodes n 1 , n 2 , n 3  and n 4  of vibration of a second predetermined frequency f 3  which would be produced when the vibrating plate is driven at the center thereof, each of all of said line nodes extending in parallel to the shorter sides of the rectangular shape of the vibrating plate.   
     
     
       2. A loudspeaker as claimed in claim 1, further comprising damper means for damping resonant vibrations caused by asymmetrical positioning of said first and second magnetic drives longitudinally of said vibrating plate, said damper means being secured to a portion of the vibrating plate where the amplitude of said resonant vibrations is at a maximum value. 
     
     
       3. A loudspeaker as claimed in claim 1, wherein said first magnetic drive is used to drive at one of the line nodes m 1  and m 2  and one of the line nodes n 1 , n 2 , n 3  and n 4  while said second magnetic drive is used to drive at the other of said line nodes m 1  and m 2  and another one of said line nodes n 1 , n 2 , n 3  and n 4 . 
     
     
       4. A loudspeaker as claimed in claim 3, wherein each of the voice coil bobbins, respectively constituting said first and second magnetic drives, is formed with a cut-out means to make it contact with the vibrating plate at such locations as corresponding to the associated line nodes. 
     
     
       5. A loudspeaker as claimed in claim 3, wherein each of the voice coil bobbins, respectively constituting said first and second magnetic drives, is coupled to the vibrating plate through the intervention of a tube member. 
     
     
       6. A loudspeaker as claimed in claim 3, wherein said one of the line nodes m 1  and m 2  is m 1  and said one of the line nodes n 1  to n 4  is n 1  or n 2 , and wherein said other of the line nodes m 1  and m 2  is m 2  and said another one of the line nodes n 1  to n 4  is n 4  or n 3 . 
     
     
       7. A loudspeaker as claimed in claim 3, wherein said first and second magnetic drives are used to drive asymmetrically the vibrating plate at the line nodes m 1  and n 1  or n 2  and the line nodes m 2  and n 3  or n 4   
     
     
       8. A loudspeaker as claimed in claim 7, further comprising a damper means for damping resonant vibrations caused by asymmetrical positioning of said first and second magnetic drives longitudinally of said vibrating plate, said damper means being secured to a portion of the vibrating plate where the amplitude of said resonant vibrations is at a maximum value. 
     
     
       9. A loudspeaker as claimed in claim 1, further comprising a filter element electrically connected in parallel to one of the voice coils forming the respective first and second magnetic drives for suppressing the peak value of sound pressures. 
     
     
       10. A loudspeaker as claimed in claim 9, wherein said filter element is a capacitor. 
     
     
       11. A loudspeaker as claimed in claim 9, wherein said filter element is an inductor. 
     
     
       12. An electrodynamic loudspeaker having: a basket;   a generally rectangular flat vibrating plate having two pairs of opposite sides, the sides of one of said pairs being longer than the sides of the other said pair supported by said basket through a flexible edge member; and   magnetic drive means consisting only of, a first magnetic drive fixedly coupled to the vibrating plate to drive said vibrating plate at a first location corresponding to one of four nodes n 1 , n 2 , n 3  and n 4  of a free mode of vibration, and   a second magnetic drive fixedly coupled to the vibrating plate to drive said vibrating plate at a second location corresponding to another one of said four nodes.     
     
     
       13. A loudspeaker as claimed in claim 12, wherein said one of the four nodes is n 4  and said another one of the four nodes is n 3 . 
     
     
       14. A loudspeaker as claimed in claim 12, wherein said one of the four nodes is n 4  and said another one of the four nodes is n 2 . 
     
     
       15. A loudspeaker as claimed in claim 12, further comprising a damping member secured to a portion of the vibrating plate where the amplitude of an asymmetric mode of vibration having three nodes attains a maximum value. 
     
     
       16. A loudspeaker as claimed in claim 12, further comprising a passive element electrically connected in parallel to one of the voice coils forming the respective magnetic drives for flattening a sound pressure versus frequency characteristic of the loudspeaker. 
     
     
       17. A loudspeaker as claimed in claim 16, wherein said passive element is a capacitor. 
     
     
       18. A loudspeaker as claimed in claim 16, wherein said passive element is an inductance element. 
     
     
       19. A loudspeaker as claimed in claim 12, wherein said first and second magnetic drives are used to symmetrically drive the vibrating plates at the nodes n 1  and n 2  and the nodes n 3  and n 4 , respectively.